X-ray astronomy infers the properties of celestial sources from their X-rays. It requires instruments above the strongly absorbing layers of Earth's terrestrial atmosphere. Riccardo Giacconi's 2002 Nobel lecture connects the early rocket detections to later grazing-incidence X-ray optics, which collect photons over a large entrance area onto a small detector.[ref]
The Dawn of X-Ray Astronomy by Riccardo Giacconi. The Dawn of X-Ray Astronomy, introduction and section 4, pp. 123–124
The measurement is an inverse problem: a count rate mixes incident photon arrival rate, detector response, and background. A point-like astronomical source produces a direction-dependent excess as the instrument scans; diffuse X-ray background contributes over many directions. Neither a count excess nor a narrow feature by itself determines the emission mechanism. The useful progression is from detecting an excess, to locating it, to measuring its spectrum and light curve.
X-ray astronomy is a branch of astronomy that studies astronomical objects and phenomena that emit X-rays, which are high-energy electromagnetic waves. Because X-ray radiation is absorbed by Earth's atmosphere, X-ray observations cannot be made from the ground. Instead, X-ray astronomers utilize satellites and space-based observatories to detect and analyze these high-energy emissions.
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